1. Field
Disclosed herein is a method for the production of magnetic powder composite cores pressed from a mix of alloy powder and binder. Also disclosed herein is a powder composite core.
2. Description of Related Art
In powder composite cores of this type, low hysteresis and eddy-current losses are desired. The powder is typically supplied in the form of flakes provided by comminuting a soft magnetic strip produced using melt spinning technology or by means of water atomisation. These flakes may, for example, have the form of platelets. While flakes of pure iron or iron/nickel alloys are so ductile that they are plastically deformed under the influence of the compacting pressure and result in pressed cores of high density and strength, flakes or powders of relatively hard and rigid materials require binders if cores of adequate strength are to be produced. If the flakes are compacted to form a magnet core using a pressing tool at high pressure, it may be necessary to prevent the expansion of the core due to spring back of the flakes in the subsequent relaxation process by adding a binder. This expansion would result in an undesirable reduction of the density of the core or even in its breaking apart and destruction.
If the magnet cores have a minimal expansion tendency, as in the case of ductile crystalline alloys, mineral binders, for example based on water-soluble silicates, can be used. These binders develop their full effect only after the magnet cores have been dried outside the pressing tool. At this point, the magnet core reaches its final strength.
If, however, the magnet cores tend to expand due to spring back of the flakes, as is typical for cores made of rapidly solidifying, amorphous or nanocrystalline alloys, the binder has to become effective before the pressed core is removed from the tool. For this reason, thermosetting materials which cure within the pressing tool itself are typically used as binders. These, however, have the disadvantage that they are not sufficiently heat-resistant to allow the magnet core to be heat treated in order to adjust its magnetic properties.